This invention relates to a method of welding parts of a titanium alloy fundamentally in the manner of butt welding.
Titanium is a relatively light metal with a specific gravity of 5.54 g/cm.sup.3. Because of a relatively high value of specific strength (strength/density) and excellence in heat resistance and corrosion resistance, the use of titanium has been increasing in the area of chemical processing equipment and also in many other areas. Moreover, the addition of certain alloying elements to titanium gives high strength titanium alloys that are very high in specific strength, corrosion resistance and heat resistance and suited to engineering material also in other properties. Accordingly the application of such titanium alloys has been broadening particularly in the aerospace industries. For example, titanium alloys are widely used in the skins of aircraft and the motor cases of rockets.
In manufacturing a structure of a high strength titanium alloy, often there is the need of butt-welding parts of the titanium alloy, and it is prevalent to perform the butt welding in this case by an electron beam welding process. However, the weld metal section (a section brought to molten state during the welding process and solidified again) given by this welding method is liable to become considerably lower in toughness than the base metal, and it is difficult to improve the mechanical properties of this weld metal section by a postwelding heat treatment and sometimes, depending on the type of the titanium alloy, the weld metal section becomes more brittle by heat treatment. It is also conventional to perform butt welding of titanium alloy parts by a so-called TIG arc welding process, which is an inert-gas shielded-arc welding process using a nonconsumable tungsten electrode, by using a commercially pure titanium rod as filler metal. However, the weld metal section given by this welding method is liable to retain a portion of the pure titanium in the unalloyed state and therefore to become considerably lower in strength than the base metal.